Customer has an issue with a prefix that have two next-hops installed causing a loop in the network, Customer is using "protect core", this option installs a precomputed next hop in the RIB and FIB with higher weight as a backup. Disabling "protect core" resolves the issue.

For a certain prefix, you will notice the following:

1- The routing table shows that the active path has two outgoing interfaces.

2- Forwarding table shows that both interfaces are installed.

3- Looking at the bgp received route it comes in with a single next-hop.

4 - this single next-hop is resolved via another next-hop which recursively resolved to 2 next-hops.

"Preserve-Nexthop-Hierarchy" knob is required when the indirect-next-hop is behind another indirect next-hop. For more details about this topic please check Mastering BGP PIC in JUNOS